Method and Apparatus for Three Dimensional Large Area Welding and Sealing of Optically Transparent Materials

ABSTRACT

Methods and systems for three dimensional large area welding and sealing of optically transparent materials are disclosed, including generating a beam of ultra-short pulses from an ultra-short pulsed laser; directing the beam to an acoustic-optic modulator to control the repetition rate of the beam; directing the beam to an attenuator after passing through the acoustic-optic modulator to control the energy of the beam; directing the beam to a focusing lens after passing through the attenuator to focus the beam between a top substrate and a bottom substrate in order to weld the top substrate to the bottom substrate, wherein the top substrate and the bottom substrate are in intimate contact; and controlling the position of the top substrate and the bottom substrate relative to the beam using a three-axis stage in order to weld the top substrate to the bottom substrate at different points. Other embodiments are described and claimed.

I. CROSS REFERENCE TO RELATED APPLICATIONS

The application is a divisional application of application Ser. No.13/239,331, filed Sep. 21, 2011, titled “Method and Apparatus for ThreeDimensional Large Area Welding and Sealing of Optically TransparentMaterials,” the contents of which are hereby incorporated by reference.

II. BACKGROUND

The invention relates generally to the field of three dimensional largearea welding and sealing of optically transparent materials. Moreparticularly, the invention relates to welding and sealing with anultra-short pulsed (USP) laser.

III. SUMMARY

In one respect, disclosed is an apparatus for sealing and weldingoptically transparent substrates comprising: an ultra-short pulse laserto produce a beam of ultra-short laser pulses, wherein the beamcomprises a pulse duration, a wavelength, a repetition rate, and a pulseenergy; an acoustic-optic-modulator at the output of the ultra-shortpulse laser to control the repetition rate of the beam; an attenuator tocontrol the energy of the beam after passing through the acousticmodulator; a focusing lens to focus the beam between a top substrate anda bottom substrate, wherein the top substrate and the bottom substrateare substantially in contact; and a three-axis stage to control theposition of the top substrate and the bottom substrate relative to thebeam.

In another respect, disclosed is a method for sealing and weldingoptically transparent substrates, the method comprising: generating abeam of ultra-short pulses from an ultra-short pulsed laser, wherein thebeam comprises a pulse duration, a wavelength, a repetition rate, and apulse energy; directing the beam to an acoustic-optic modulator tocontrol the repetition rate of the beam; directing the beam to anattenuator after passing through the acoustic-optic modulator to controlthe energy of the beam; directing the beam to a focusing lens afterpassing through the attenuator to focus the beam between a top substrateand a bottom substrate in order to weld the top substrate to the bottomsubstrate, wherein the top substrate and the bottom substrate aresubstantially in contact; and controlling the position of the topsubstrate and the bottom substrate relative to the beam using athree-axis stage in order to weld the top substrate to the bottomsubstrate.

Numerous additional embodiments are also possible.

IV. BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and advantages of the invention may become apparent uponreading the detailed description and upon reference to the accompanyingdrawings.

FIG. 1 is a schematic diagram of a set up for USP laser welding andsealing of optically transparent materials, in accordance with someembodiments.

FIG. 2 is a schematic illustration of the USP laser welding and sealingof optically transparent materials by focusing the laser beam in theinterface between the substrates, in accordance with some embodiments.

FIGS. 3( a) and (b) are a schematic illustrations showing an isotropicview and a cross sectional view, respectively, of a fixture for USPlaser welding and sealing of optically transparent materials, inaccordance with some embodiments.

FIG. 4 is a schematic illustration of the focal position step adjustmentfor USP laser welding and sealing of optically transparent materials, inaccordance with some embodiments.

FIG. 5 is a microscopic view of welded and non-welded regions of fusedsilica, in accordance with some embodiments.

FIGS. 6( a) and (b) are SEMs of single line welds of fused silica with a0.61 μJ laser pulse energy at a 1 mm/s scan speed after breaking theweld, where FIG. 6( a) shows the welding surface of the top substrateshowing grooves or recesses where the welding seam has peeled off, andFIG. 6( b) shows the welding surface of the bottom substrate showingbumps or protrusions where the welding seam remains, in accordance withsome embodiments.

FIG. 7 is an SEM of single line welds of fused silica with a 0.61 μJlaser pulse at 1 mm/s with the weld seam floating in the air above thesurface, in accordance with some embodiments.

FIGS. 8( a) and (b) are SEMs of multi line weld regions of fused silicawith a 0.61 μJ laser pulse at 1 mm/s after breaking the weld, where FIG.8( a) shows the welding surface of the top substrate and FIG. 8( b)shows the welding surface of the bottom substrate, in accordance withsome embodiments.

FIG. 9 shows two multi line weld regions in a sample, in accordance withsome embodiments.

FIGS. 10( a) and (b) show a one-edge-sealed glass substrate weld, whereFIG. 10( a) shows the welded regions visible by LED side illuminationand FIG. 10( b) shows the attachment of the bottom plate as exhibited bythe top plate being held by tweezers, in accordance with someembodiments.

FIGS. 11( a) and (b) show a four-edge-sealed fused silica weld, whereFIG. 11( a) shows the top view with interference fringes visible forthose non-welded regions and no interference fringes visible for thosesealed seams and FIG. 11( b) shows the four welded seams crossing eachother visible by LED backlight illumination, in accordance with someembodiments.

FIGS. 12( a) and (b) show microscopic views of four-edge sealing of twofused silica samples, where FIG. 12( a) shows the one of the seamscomposed of multiple welding lines and FIG. 12( b) shows theintersection of two seams, in accordance with some embodiments.

FIG. 13 illustrates the hermetic sealing of the central region of thesample of FIGS. 11( a) and (b) after immersion in water, in accordancewith some embodiments.

FIG. 14 shows a microscopic view of USP laser fused silica single linewelds at different scanning speeds and the same pulse energy beforeseparation, in accordance with some embodiments.

FIG. 15 shows a microscopic view of USP laser fused silica single linewelds at different scanning speeds and the same pulse energy afterseparation, in accordance with some embodiments.

FIG. 16 is a block diagram illustrating a method for three dimensionallarge area welding and sealing of optically transparent materials withultra-short pulsed laser, in accordance with some embodiments.

While the invention is subject to various modifications and alternativeforms, specific embodiments thereof are shown by way of example in thedrawings and the accompanying detailed description. It should beunderstood, however, that the drawings and detailed description are notintended to limit the invention to the particular embodiments. Thisdisclosure is instead intended to cover all modifications, equivalents,and alternatives falling within the scope of the present invention asdefined by the appended claims.

V. DETAILED DESCRIPTION

One or more embodiments of the invention are described below. It shouldbe noted that these and any other embodiments are exemplary and areintended to be illustrative of the invention rather than limiting. Whilethe invention is widely applicable to different types of systems, it isimpossible to include all of the possible embodiments and contexts ofthe invention in this disclosure. Upon reading this disclosure, manyalternative embodiments of the present invention will be apparent topersons of ordinary skill in the art.

Development of techniques for welding transparent materials is of greatimportance in a number of application areas, such as life science,sensing, optoelectronics, and MEMS packaging. The joining of two or moreoptically transparent materials, such as glasses, is useful and desiredin device level fabrication, such as micro-fluidic systems whereflexible, precise, strong, and tight sealing are required. The fieldlacks an effective method for transparent material welding with highflexibility, non-invasive, and single-step operation. Various joiningand welding techniques have been developed and reported; however, eachwith specific properties has reached its limit in terms of flexibility,reproducibility, and preparation and cycle time and is useful onlywithin a limited application range. Joining technologies such as bindingor gluing using adhesives suffer from mismatch between the thermalexpansion coefficients of transparent material and the adhesive and thelong term stability of the bonds. Oxygen and moisture graduallypenetrate the interior of the component and affect its function. Thelimited durability and the temperature sensitivity of glued connectionsare problems, especially for components used in the medical sector. Themost common bonding technique for glass is optical contacting and thisis an adhesive-free process at which two ultra flat and ultracleansurfaces with the same curvature are bound together by the molecularattraction between the surface atoms. But the bond strength is typicallyvery weak (a few kPa) and is highly susceptible to impact load. Anothertechnique, laser welding using Continuous Wave (CW) lasers or longpulsed lasers is based on linear absorption—the laser beam penetratesthe top sample and is focused on the top surface of the bottom sample.In this technique, cracks develop during the cooling period. Since thistechnique is based on linear absorption, it requires that one of thesamples to be joined be transparent and the other sample to be absorbingat the wavelength of the laser used. Thus, the selection of materials tobe joined is limited and it cannot be carried out for non-absorbingmaterials such as glasses. Furthermore, sealing and packaging ofsemiconductor material is very important and critical in producinghighly reliable semiconductor devices. Traditional welding methods, suchas arc welding and brazing, generate heat-affected zones (HAZ) andresult in a reduction of the tensile strength and toughness of thematerials. Residual stresses that develop as the materials cool downalso reduce the strength of the welded joints. Thus, the welding processmust be optimized (by optimizing heat generation, compositions, andcooling rates) and post-welding treatments are also often needed torelieve residual stresses and make the microstructure of the welds moreuniform. Therefore, it would be useful to develop a simple andcost-effective method of welding and sealing optical transparentmaterials with high precision.

There has been some work on welding of optical transparent materialsusing ultra-short pulsed lasers, specifically by Itoh et al.(US2010/0047587) and Bovatsek et al. (US2010/0084384). But these systemsonly achieve good welding between substrates and components with smallarea and are thus limited in their use for industrial applications. Theyhave demonstrated welding with bonded area of less than 0.2 mm² forsimilar and dissimilar materials. They also require that the substrateshave high precision flatness and that the gap between the substrates tobe less than a quarter wavelength for successful welding. To achievethis, Itoh used a hemispherical projection to achieve only a small areaof optical contact between substrates. This invention overcomes thislimitation and demonstrates the capability to weld similar anddissimilar materials using ultra-short pulsed lasers over 10 mm² areasbetween the two substrates. This invention increases the potential forlaser welding of applications in semiconductor industry, precision opticmanufacturing, and aerospace engineering using USP lasers.

The embodiment or embodiments described herein may solve theseshortcomings as well as others by proposing a simple and cost-effectivemethod of welding and sealing optical transparent materials over a largearea with high precision. Additionally, the embodiments may be used forthree dimensional large area welding.

The term “ultra-short pulse laser” or “USP laser” refers to a laser beamgenerated in the form of extremely brief and finite intervals, i.e.,pulses. USP lasers used herein are characterized by various parameters.For instance, “pulse duration” refers to the length of time of eachinterval wherein the laser beam is generated. A suitable pulse durationmay be between about 1 fs to about 50 ps. The parameter “pulse energy”refers to the amount of energy concentrated in each interval wherein thelaser beam is generated. Pulse energy may be between about 0.01 μJ toabout 100 mJ. The single pulse fluence refers to the pulse energydelivered over the focal spot size. It may be between 0.01 J/cm² to 100J/cm². The parameter “repetition rate” refers to the number of pulsesthat are emitted per second, and indirectly relates to the time betweeneach pulse emission, i.e., the length of time between each pulse. Therepetition rate may be between about 1 kHz and about 100 MHz. The USPlaser beam of the invention may be of any wavelength in theelectromagnetic spectrum from deep UV to IR range. The wavelength may bebetween about 100 nm to about 10 μm. Another parameter used tocharacterize the USP laser is “scanning speed,” which refers to the rateat which the USP laser moves across the surface of a material. Thescanning speed may be, for example, between about 0.01 mm/s and about500 mm/s. The numerical aperture used for focusing of the USP laser beammay be between 0.05 to 0.9. The “focus spot size” refers to the diameterof the USP laser beam. This diameter may be, for example, between about400 nm and about 100 μm.

The methods of the invention described herein take advantage of theunique effects of USP lasers. When USP laser pulses are tightly focusedonto optically transparent materials, the high intensity inside thefocal volume due to the tight focusing of the short laser pulse willinduce multi-photon or tunneling ionization and subsequent avalancheionization occurs, and finally this nonlinear absorption results in thecreation of hot plasma and subsequent heating to the surroundingmaterials. Therefore, the USP laser can act as a local heat source inthe volume. Because the plasma generation happens within a small focalregion and the cooling time is short, high repetition rate laser systemsoperating in the MHz range are generally used, which leads to themelting of the focal region due to heat accumulation of successivepulses. The melting and solidification of the material results in thegeneration of covalent bonds if the laser focus is located at theinterface between two adjacent samples. Furthermore, the highlylocalized heat generation minimizes the thermal induced stress and caneffectively suppress the development of the thermally induced cracks.

Through nonlinear absorption, USP lasers can deposit energy into anextremely well-defined region within a bulk transparent material, andproduce a range of features —causing a permanent refractive index changethat enable optical waveguiding, melting, and subsequent welding for twoor more stackable materials, or voids that can be used for micro-fluidicfabrication. The property of USP lasers of the invention to processoptically transparent material without transferring energy and damagingsurrounding material is ideal for precision methods such as bonding,micro-channel fabrication, etc. The term “precision” relates toapplication of the USP laser without damaging material surrounding thetarget site.

Optically transparent is the physical property of allowing light to passthrough a material. Transparent in the definition means that when a USPlaser beam is incident on the material, the substrate is transparent tothe extent that a nonlinear absorption phenomenon occurs. Accordingly,whether the substrate to be welded is transparent with respect tovisible light is not a concern. In other words, if a substrate materialis determined to be opaque for visible light, such a substrate is stillconsidered to be ‘transparent’ material in the definition of the presentinvention as long as USP laser beam can generate nonlinear absorption inthe material after penetrating a certain depth of the material. Thetransparent material can be selected from the group consisting of alltypes of glasses, polymers, silicon, germanium, gallium, galliumarsenide, silicon carbide, arsenide, indium gallium arsenide and otheralloy of multiple semiconductor compounds.

One particular aspect of the invention provides a method of weldingoptically transparent materials with high precision with a simple setup, comprising applying a USP laser beam to the interface between twostackable substrates. The beam may be initially focused at a first sitein the interface, such that the beam generates welding at the site. TheUSP laser may then be applied to a second site above or adjacent a fewmicrons to the first site, wherein the laser welds the materials at thesecond site. This process may be repeated for additional sites acrossthe interface until the welding seam is strong enough to preventseparation. Here the weld is defined as a localized fusion oftransparent materials produced by nonlinear absorption to suitabletemperatures. Pressure may be applied to the two stacked substrates andno filler material is used or required.

A problem in the conventional laser welding method is that it isnecessary to accurately form the focal point of the ultra-short pulselaser beam on the interface of the two substances that are to be joined,but knowing the position where the focal point of the laser beam isformed is extremely difficult since the substances to be joined aretransparent to the laser beam. In contrast, when a USP laser beam havinga pulse width on the order of a femtosecond to a picosecond is incidenton a transparent substance such as glass, the laser beam has a basicallyGaussian spatial intensity distribution. Therefore, the refractive indexin the center portion where the light intensity is high in a nonlinearmedium is higher than in other areas, and the medium itself acts as apositive lens. For this reason, a self-focusing effect occurs in whichthe incident light becomes focused to a point, and in a USP laser beam,the beam diameter is thought to become minimal after the USP laser beamhas propagated a finite distance in the transparent substance. However,in actuality, photoionization occurs in the medium, plasma in whichelectrons and ions in the substance move freely is formed, and therefractive index of the medium decreases. When the tertiary nonlinearoptical effect and the reduction in the refractive index due to plasmaformation counterbalance each other, the USP laser beam propagates apredetermined distance while maintaining a certain beam diameter. Thisphenomenon is called filamentation, and the area where filamentationoccurs is called a filament area. Destructive damage is thought to notreadily occur in the filament area due to the plasma density being keptconstant.

Another method to solve the focusing position determination problem isto use multi-line scanning with long focal depth (smaller numericalaperture) and to use multi-line scanning with the same objective lensbut with the focus position step adjustment for each repeat. Themulti-line scanning is capable of covering a larger focal depth withfocal position step adjustment for each repeat. This is also practicalfor industrial applications since the scanning speed is high enough. Thefocal position step adjustment starts from a deeper focus and movetowards the focusing lens for each step. The step adjustment value canbe from 5 μm to 50 μm. The high repetition rate and the pulse overlapresults in an accumulated thermal heating between the materialmodification created by the previous pulse and the subsequent pulses forthe same focal position. This gives a fast welding speed and arelatively smooth welding region. The nonlinear absorption processeffectively confines the absorbed energy near the welding interface andminimizes the damage and stress formation to the rest of the material,so fine welding lines or regions can be obtained with the USP laser.

FIG. 1 is a schematic diagram of a set up for USP laser welding andsealing of optically transparent materials, in accordance with someembodiments.

In some embodiments, a USP laser 105 emits laser pulses 110 which aredirected through an Acoustic-Optic Modulator 115 which is controlled bya delay generator 120 to change the pulse repetition rate. The laserpulses 110 are then apertured with a shutter 125 before they passthrough an attenuator 130 which controls the pulse energy. The laserpulses are then reflected by two mirrors 135 and one dichroic mirror 140and subsequently focused by an objective lens 145. The laser pulses 110are focused at the interface between the two substrates of the sample150 and generate nonlinear absorption so that the two substrates arewelded together by the generation of a filament area resulting from theself-focusing effect of the USP laser pulses in the top substrate. Amechanical fixture is used to hold the samples on a motorized 3-axismotion stage system 155 with two tilting adjustment for alignment.Depending whether clamping force is needed or not, the fixture alsoserves as a clamping device to generate close contact between twosubstrates when necessary. A computer 160 is used to control the delaygenerator 120 and to view and capture live images from the CCD 165 whichmonitors the sample through the dichroic mirror 140 as the sample iswelded. FIG. 2 shows a close up of the weld region 210 that isgenerated. The USP laser pulses 110 are directed through the objectivelens 145 and focused on the interface between the top substrate 215 andthe bottom substrate 220.

In some embodiments, a fixture is used to decrease the air space betweenthe top substrate and the bottom substrate. FIG. 3( a) shows anisotropic view of one such fixture. Two transparent material substrates310 are stacked together and a cylindrical lens 315 or some other objectthat creates a pressure region under the bottom plate is placedunderneath the bottom substrate. A cylindrical lens, or portion of acylinder, will create a linear pressure region whereas other objectslike a torus would create a circular pressure region between the twosubstrates. Other shaped raised objects created from segments ofcylinders and tori can be used to create any arbitrary shaped pressureregions. Segments of cylinder will create linear regions and segments oftori will create arc regions. A cushion or some other malleable materialon top of the cylindrical lens 315 may be used to extend the pressurearea and to keep the pressure uniform over the area. By using anextended pressure region, it is possible to weld longer lengths andsubsequently larger total areas. The sample is pressed together betweena top plate 320 and a bottom plate 325. The plates can be made oftitanium or other rigid material. The plates are held together withscrews and nuts (not shown) through the holes 330 in the top plate 320and bottom plate 325 so that a close and uniform interface line isgenerated along the cylindrical axis direction. The gap between the twosubstrates is usually less than a quarter wavelength along the uniforminterface line as can be observed as an optical interference patternusing the CCD. FIG. 3( b) shows a cross sectional view of the samplefixture. In some embodiments, a cushion 335 may be placed between thecylindrical lens 315 and the bottom of the bottom substrate 220. Thecushion 335 or some other malleable material is used to extend thepressure area and to keep the pressure uniform over the area, meanwhileit can also prevent the over stressing or fracturing of the bottomsubstrate.

FIG. 4 is a schematic illustration of the focal position step adjustmentfor USP laser welding and sealing of optically transparent materials, inaccordance with some embodiments.

In some embodiments, focus position is adjusted to solve the focusingposition determination problem. The focal depth is first positionedthrough and into the bottom substrate 220 as represented in step 1. Thefocus is then adjusted away from the bottom substrate 220 by some stepadjustment value, Δz, which may range from 5 μm to 50 μm. The stepadjustment is repeated until the focal depth extends into the bottomportion of the top substrate 215 as represented in step 3. FIG. 4 showsthis process in three steps, but any number of steps may be used tofacilitate the welding of the two substrates.

FIG. 5 is a microscopic view of welded and non-welded regions of fusedsilica, in accordance with some embodiments.

In some embodiments, an array of linear welds may be done to weld aregion together. In FIG. 5, the welded region 510 can be distinguishedfrom the non-welded region 515 of a fused silica sample. The substratesin FIG. 5 are still welded together, whereas in FIGS. 6( a) and (b), thesubstrates have been separated to break apart the weld. In FIGS. 6( a)and (b), the substrates had dimensions of 10 mm×10 mm with a 0.5 mmthickness and were welded with single line welds using USP laser pulseswith 750 fs pulse duration, 1030 nm wavelength, 1 MHz repetition rate,0.61 μJ pulse energy, and 1 mm/s scanning speed. FIG. 6( a) shows thewelding surface of the top substrate showing grooves—welding seam peeledoff, and FIG. 6( b) shows the welding surface of the bottom substrateshowing bumps—welding seam remains. The welding seam for each singleline can be clearly seen and most of the welding seam remains on thebottom substrate since the bottom substrate is fixed and the topsubstrate is peeled off manually. The laser beam was focused using a 20×objective lens with a 0.4 numerical aperture. The focal spot size of thelaser pulse was calculated to be 5 μm. FIG. 7 shows an enlarged SEM viewof the top two weld seams from FIG. 6( b). The welded seams can be seenfloating in the air of the surface of the substrate due to the manualpeeling of the top substrate from the bottom substrate.

In some embodiments, any arbitrary shaped weld may be produced, such asa circle, a square, a rectangular, a hexagon, a triangle, etc.Furthermore, the technique may also be applied to seal any shape oftransparent material shape as long as the substrates surface flatnessand roughness are good enough to obtain an intimate contact so that theinterface gap between two substrates is shorter than the filamentationlength. This may be accomplished with the help of clamping pressure insome cases. For example, the substrate shape can be square, rectangular,circular, triangular, hexagonal, etc. Additionally, the bottom substratedoes not have to be transparent, thus making it possible to weld a glasssubstrate atop a metal substrate or any other non-transparent substrate.

FIGS. 8( a) and (b) are SEMs of multi line weld regions of fused silicawith a 0.61 μJ laser pulse at 1 mm/s after breaking the weld, where FIG.8( a) shows the welding surface of the top substrate and FIG. 8( b)shows the welding surface of the bottom substrate, in accordance withsome embodiments.

In some embodiments, multiple lines are welded close together to weld anentire region. FIGS. 8( a) and (b) show an SEM view of multi linewelding regions of fused silica after breaking the weld. Both of thesubstrates have dimensions of 10 mm×10 mm with a 0.5 mm thickness. TheUSP laser pulses had a 750 fs pulse duration, a 1030 nm wavelength and a1 MHz repetition rate. The pulse energy used was 0.61 μJ and thescanning speed was 1 mm/s. FIGS. 8( a) and (b) illustrate the twosurfaces of the same welding position. FIG. 8( a) shows the weldingsurface of the top substrate after separation and FIG. 8( b) shows thewelding surface of the bottom substrate after separation. In total,there are 40 lines which were repeated three times for each line. Thepitch between the lines is 5 μm which resulted in a total welding areasize of 0.1 mm². The protrusion 810 corresponds to the recess 815 andthe protrusion 820 corresponds to the recess 825. There is a one-to-onecorrespondence between the protrusions or bumps and the recesses orindentions of the substrates which shows the effective welding of thetwo substrates.

FIG. 9 shows two multi line weld regions in a sample, in accordance withsome embodiments.

In some embodiments, one-edge sealing of transparent material isaccomplished by using a USP laser. FIG. 9 is a picture showing tworegions of area scanning. The substrates have dimensions of 10 mm×10mm×1 mm. Where the substrates have been effectively sealed together,there are no visible interference fringes. The sample shows that it wascompletely along the entire length. The weld comprises two area sectionsof 500 μm×10 mm. The top area 910 was scanned with 0.86 μJ pulses andrepeated once with 0.62 μJ pulses at a 10 μm focal position change. Thetop area 910 comprises about 100 lines with a 5 μm pitch scanned at 1mm/s for a total area of 5 mm². The lower area 915 was scanned with 0.62μJ pulses at 1 mm/s followed by different repeat scans. The first 250 μmclosest to the top area 910 were repeat scanned 3 times with a 10 μmfocal position change. The next 125 μm were repeat scanned 2 times andthe bottom 125 μm was not repeat scanned. The total area scanned in thelower area 915 was also 5 mm².

FIGS. 10( a) and (b) show a one-edge-sealed glass substrate weld, whereFIG. 10( a) shows the welded regions visible by LED side illuminationand FIG. 10( b) shows the attachment of the bottom plate as exhibited bythe top plate being held by tweezers, in accordance with someembodiments.

In some embodiments, one-edge sealing of glass substrates isaccomplished by using a USP laser. FIG. 10( a) clearly shows two sealedregions that run from edge to edge. They are visible as the two bands1010 and 1015 resulting from LED side illumination. FIG. 10( b) showsthat if only the top glass substrate is held with a pair of tweezers,the force of gravity does not separate the two glass substrates as theyhave been effectively welded.

FIGS. 11( a) and (b) show a four-edge-sealed fused silica weld, whereFIG. 11( a) shows the top view with interference fringes visible forthose non-welded regions and no interference fringes visible for thosesealed seams and FIG. 11( b) shows the four welded seams crossing eachother visible by LED backlight illumination, in accordance with someembodiments.

In some embodiments, all four edges of the sample may be welded fromedge to edge to seal two glass slides. The USP laser pulses areinitially focused in the interface along one edge of the substrate suchthat the USP laser pulses generate one continuous weld seam along oneedge. The USP laser pulses may then be applied to a second edge adjacentto the first welded edge to generate a second weld seam. This processmay be repeated along the four edges of the transparent materialsubstrate. FIG. 11( a) is a photo of two 10 mm×10 mm×1 mm silica samplesthat were welded from edge to edge on all four sides with USP laserpulses having 750 fs pulse duration, 1030 nm wavelength, 1 MHzrepetition rate, 0.61 μJ pulse energy, and 1 mm/s scanning speed. Eachedge comprises a weld area of 2.5 mm² for a total weld area for thesample of 10 mm². FIG. 11( a) shows the top view with interferencefringes seen with reflection for those non-welded regions and nointerference fringes seen for the sealed seams. FIG. 11( b) shows atransmission view of the four welded and sealed seams, 1110, 1115, 1120,and 1125 crossing each other visible by LED backlight illumination. Eachseam was welded with three repeat scans. Generally if the first weldingseam is effective, the rest of the seams will be effective since opticalcontact can be obtained easily. FIG. 12( a) shows a microscopic view ofone of the edges from the sample in FIGS. 11( a) and (b) and FIG. 12( b)shows a microscopic view of two crossed sealed edges. The images showthat the welds are effective in sealing the two substrates together. Tofurther show the hermetic sealing of the two substrates, the sample wasimmersed in water to see whether water would penetrate the sealedregion. FIG. 13 shows that water did not penetrate into the centralregion of the sample due to the surrounding four weld seams. The purposeof the sealing may not only be to contain a liquid, but can also be usedto seal against a gas. Additionally, the bottom surface of the top glassslide or the top surface of the bottom slide may have some coating thatis protected by the welding of a hermetically sealed region. The coatingcan be on one or both of the slides. The slides can comprise anyoptically transparent substrate or filter that has a coating that needsto be protected from the environment. This embodiment of the inventionenables the sealing of filters with coatings for a variety of industrialapplications.

In some embodiments, the scan speed may be adjusted to achieve thedesired effective weld. FIG. 14 shows a microscopic view of USP laserfused silica single line welds with a pulse energy of 0.95 μJ but withdifferent scanning speeds. Weld 1410 was scanned at 0.1 mm/s, weld 1415was scanned at 0.2 mm/s, weld 1420 was scanned at 0.5 mm/s, weld 1425was scanned at 1.0 mm/s, and weld 1430 was scanned at 2.0 mm/s.Interference fringes can be seen between the welds. Although the weldline width becomes smaller for larger scanning speeds, the welding seamis uniform even for 10 mm/s. The welding seam width and strength can becompensated by using higher pulse energy or higher repetition rates.High speed welding and sealing up to 500 mm/s makes the weldingtechnique applicable for industrial production. FIG. 15 shows themicroscopic view of one of the substrates from the sample of FIG. 14after the sample has been manually separated. The welding seams 1410,1415, 1420, 1425, and 1430 are clearly visible.

In some embodiments, more than two substrates can be stacked and weldedonto each other. To seal a three-layer transparent material substrate,the bottom two substrates are first sealed by focusing the USP laserpulses between the interface between the bottom two substrates. Afterthe bottom two substrates are sealed, a third substrate may be sealedonto the sealed two substrates. Generally, the sealing sequence formulti-layer sealing is from bottom to top so that the USP laser pulsesdo not need to be focused too deep, thus lessening the laser beam lossand distortion.

FIG. 16 is a block diagram illustrating a method for three dimensionallarge area welding and sealing of optically transparent materials withultra-short pulsed laser, in accordance with some embodiments.

Processing begins at block 1605 where an ultra-short pulsed laser isused to generate a beam of ultra-short pulses. At block 1610, the beamis directed to an acoustic-optic modulator to control the repetitionrate of the beam. After passing through the acoustic-optic modulation,at block 1615, the beam is directed to an attenuator to control theenergy of the beam. After passing through the attenuator, at block 1620,the beam is directed to a focusing lens to focus the beam between a topsubstrate and a bottom substrate in order to weld the top substrate tothe bottom substrate. Finally, at block 1625, a three-axis stage is usedto control the position of the top substrate and the bottom substraterelative to the beam in order to weld the top substrate to the bottomsubstrate at different points. At block 1630, additional substrates canbe welded and sealed by the recurrence of the process in blocks 1620 and1625 to create three dimensional large area welds and seals of opticallytransparent materials.

The previous description of the disclosed embodiments is provided toenable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

The benefits and advantages that may be provided by the presentinvention have been described above with regard to specific embodiments.These benefits and advantages, and any elements or limitations that maycause them to occur or to become more pronounced are not to be construedas critical, required, or essential features of any or all of theclaims. As used herein, the terms “comprises,” “comprising,” or anyother variations thereof, are intended to be interpreted asnon-exclusively including the elements or limitations which follow thoseterms. Accordingly, a system, method, or other embodiment that comprisesa set of elements is not limited to only those elements, and may includeother elements not expressly listed or inherent to the claimedembodiment.

While the present invention has been described with reference toparticular embodiments, it should be understood that the embodiments areillustrative and that the scope of the invention is not limited to theseembodiments. Many variations, modifications, additions, and improvementsto the embodiments described above are possible. It is contemplated thatthese variations, modifications, additions, and improvements fall withinthe scope of the invention as detailed within the following claims.

1. An apparatus for sealing and welding optically transparent substratescomprising: an ultra-short pulse laser to produce a beam of ultra-shortlaser pulses, wherein the beam comprises a pulse duration, a wavelength,a repetition rate, and a pulse energy; an acoustic-optic-modulator atthe output of the ultra-short pulse laser to control the repetition rateof the beam; an attenuator to control the pulse energy of the beam afterpassing through the acoustic modulator; a focusing lens to focus thebeam between a top substrate and a bottom substrate, wherein the topsubstrate and the bottom substrate are substantially in contact; and athree-axis stage to control the position of the top substrate and thebottom substrate relative to the beam.
 2. The apparatus of claim 1,wherein the top substrate and the bottom substrate are held together ina fixture comprising a top plate atop the top substrate and a bottomplate below the bottom substrate, wherein the top plate and the bottomplate are mechanically coupled together to press the top substrate andthe bottom substrate together.
 3. The apparatus of claim 2, wherein thefixture further comprises a protrusion between the bottom substrate andthe bottom plate.
 4. The apparatus of claim 3, wherein the protrusioncomprises segments of a cylinder or a torus.
 5. The apparatus of claim3, wherein the bottom plate comprises the protrusion.
 6. The apparatusof claim 3, wherein the fixture further comprises a cushion between thebottom substrate and the protrusion.
 7. The apparatus of claim 1,wherein the pulse duration is in the range between approximately 1 fs to50 ps, wherein the wavelength is in the range between approximately 100nm to 10 μm, wherein the repetition rate is in the range betweenapproximately 1 kHz to 100 MHz, wherein the energy is in the rangebetween approximately 0.01 μJ to 100 mJ, and wherein the beam is scannedover the top substrate between approximately 0.01 mm/s to 500 mm/s. 8.The apparatus of claim 1, wherein the top substrate and the bottomsubstrate exhibit nonlinear absorption of the beam.
 9. The apparatus ofclaim 1, wherein the top substrate is any of glass, polymer, silicon,germanium, gallium, gallium arsenide, silicon carbide, arsenide, indiumgallium arsenide, and an alloy including at least one of these.
 10. Theapparatus of claim 1, wherein the bottom substrate is any of glass,metal, polymer, silicon, germanium, gallium, gallium arsenide, siliconcarbide, arsenide, indium gallium arsenide, and an alloy including atleast one of these.
 11. The apparatus of claim 1, wherein the topsubstrate and the bottom substrate are composed of the same material.12. The apparatus of claim 1, wherein the top substrate and the bottomsubstrate are composed of different material.